This invention relates to treating copper surfaces, and more particularly to treating such surfaces to remove oxides and other impurities from them.
This invention has particular application to treating the surface of continuous copper rod of the type that is used to produce wire by drawing the rod down to the desired wire size. Although the invention will be described for the most part in relation to its use in this type of context, it will be understood that the invention is equally applicable to treating copper surfaces having other shapes, and whether continuous or not continuous.
A system for continuously casting a copper bar, reshaping that bar into a rod, and passing the rod through several surface treatment stages is shown in Escobar et al. U.S. Pat. No. 4,754,803, which is hereby incorporated by reference herein. The surface treatment is intended to remove oxides and other impurities from the surface of the copper rod. This is very important because if the surface of the rod is not sufficiently clean, wire drawn from the rod will not be satisfactory. For example, the wire drawing operation may work the rod surface imperfections and defects into the wire being produced, thereby increasing the risk of wire breakage, increasing the electrical resistance of the wire, etc.
The rod surface treatment process shown in the Escobar et al. patent has, as background, the pickling process shown in Otto U.S. Pat. No. 2,856,275, which is also incorporated by reference herein. Thus in the Escobar et al. patent the copper surface is exposed to a mixture of oxidizing and reducing agents in an aqueous solution. For example, the oxidizing agent may be hydrogen peroxide (H.sub.2 O.sub.2), and the reducing agent may be sulfuric acid (H.sub.2 SO.sub.4). The temperature of the oxidizing/reducing solution may be in the range from about 120.degree. F. to about 160.degree. F. It is believed that, in addition to oxidizing other impurities on the copper surface, the hydrogen peroxide oxidizes red cuprous oxide (CU.sub.2 O) on that surface to cupric oxide (CuO) . Then the sulfuric acid reduces the cupric oxide to dissolved copper sulfate.
After passing through the oxidizing/reducing solution, the copper surface is rinsed by passing it through a rinse bath and spray. The final step is application of a water-based wax solution, which coats and protects the finished copper surface.
While surface treatments of the type shown in the Escobar et al. patent and described above work well, there is always room for further improvement. For example, the relatively high temperature of the oxidizing/reducing solution tends to cause substantial vaporization and thereby effective loss of hydrogen peroxide from that solution. There is also room for improvement in the cleanliness and brightness of the copper surface produced.
In view of the foregoing, it is an object of this invention to provide improved systems for pickling copper surfaces.
It is another object of this invention to provide systems for treating copper surfaces so that those surfaces are cleaner and brighter than if prior surface treatments were used.
It is still another object of this invention to reduce consumption or loss of volatile oxidizing agents such as hydrogen peroxide in copper surface treatment processes that make use of such agents.